The present invention relates to functionalized initiators useful in anionic polymerizations and processes for making and using the same.
A variety of initiators, which contain oxygen, sulfur, or nitrogen functionality, have been developed for anionic polymerization. This allows the quantitative introduction of a functional group into the head of the living polymer chain so that each growing chain contains a functional group from the initiator. See U.S. Pat. Nos. 5,496,940 and 5,600,021. Exemplary protected functionalized initiators include compounds of the following formula:
M-Z-T-(A-R1R2R3)m
and

wherein: M is an alkali metal selected from lithium, sodium and potassium; Z is a branched or straight chain hydrocarbon connecting group which contains 3-25 carbon atoms; T is selected from oxygen, sulfur, or nitrogen groups and mixtures thereof; (A-R1R2R3)m is a protecting group in which A is an element selected from Group IVa of the Periodic Table of the Elements, and R1, R2, and R3 are independently defined as hydrogen, alkyl, substituted alkyl groups containing lower alkyl, lower alkylthio, and lower dialkylamino groups, aryl or substituted aryl groups containing lower alkyl, lower alkylthio, lower dialkylamino groups, or cycloalkyl and substituted cycloalkyl groups containing 5 to 12 carbon atoms; 1 is an integer from 1 to 7; and m is 1 when T is oxygen or sulfur, and 2 when T is nitrogen.
These functionalized initiators offer numerous advantages over previous anionic polymerization initiators. Such initiators, however, have limited solubility in hydrocarbon solvents. For instance, one such initiator 3-(hexamethyleneimino)-1-propyllithium has a maximum solubility in cyclohexane of 0.30 Molar. Similarly, the maximum solubility of 3-(1,1-dimethylpropyloxy)-1-propyllithium in cyclohexane is 0.30 Molar.
The addition of at least one equivalent of a conjugated diene or an alkenyl substituted aromatic compound can increase the solubility of these initiators in hydrocarbon solutions three to ten fold. The resultant initiators are generally referred to as xe2x80x9cchain extendedxe2x80x9d functionalized initiators. See U.S. Pat. Nos. 5,527,753, 5,565,526, 5,708,092 and 5,821,307. In each case, at least one equivalent of the chain extension agent is added to the initiator, as represented by xe2x80x9cQxe2x80x9d and xe2x80x9cnxe2x80x9d in the following formula:
M-Qn-Z-T-(A-R1R2R3)m
or

wherein:
M, Z, T, A, R1, R2, R3, 1 and m are the same as defined above;
Q is an unsaturated hydrocarbyl group derived by incorporation of one or more conjugated diene hydrocarbons, one or more alkenylaromatic compounds, or mixtures of one or more dienes with one or more alkenylaromatic compounds into the M-Z linkage; and
n is an integer from 1 to 5.
Thus, prior chain extended initiators included at least one, and up to five, equivalents of the chain extension agent. The addition of one or more equivalents of the chain extension agent was beneficial for the enhancement of initiator""s solubility in hydrocarbon medium. However, despite the advantages of the xe2x80x9cchain extensionxe2x80x9d technology, some drawbacks became apparent for the commercialization of this technology.
For example, the addition of at least one equivalent of the chain extension agent increased the cost of the raw materials required for the initiator formulation. The addition of larger quantities of the chain extension agent also increased the cycle time required for the initiator synthesis in the plant. This led to increased costs of the initiators. In addition, the overall exothermicity of the process was also increased by the addition of larger quantities of the chain extension agent. This caused increased safety concerns as these processes were scaled up. Further, when greater than one equivalent of the chain extension agent was added, low filtration rates were sometimes encountered. This was due to the formation of higher oligomers during the chain extension process.
Unexpectedly, it has been found that adding less than one equivalent of a chain extension agent to a protected functionalized initiator can be sufficient to significantly increase the solubility of the initiator in hydrocarbon solutions. This is contrary to the expectation that at least one equivalent chain extension agent would be necessary to improve initiator solubility. The use of less than one equivalent chain extension agent provides several benefits, including improved economies of manufacture. In addition, use of less than one equivalent chain extension agent can minimize or eliminate oligomer formation, and the manufacturing problems, particularly on a commercial scale, associated with the same.
The present invention also provide methods for making the novel initiators as well as methods of using the same and polymers produced using the initiators. The chain extended initiators can be prepared, for example, by reacting an omega-protected functionalized haloalkyl with an alkali metal, such as lithium metal, in an inert solvent to form a composition which includes the non-chain extended initiator. The non-chain extended initiator can be recovered from reaction byproducts and excess alkali metal, and the chain extension agent added to the composition. Alternatively the chain extension agent can be added to the non-chain extended initiator composition prior to filtration